Manufacture of grids for electron discharge devices



Aug. 5, 1958 A. H. ATHERTON E L MANUFACTURE OF GRIDS FOR ELECTRON DISCHARGE DEVICES Filed Sept. 9, 1953 FIGS.

jms; ALBERT HORACE ATHERTON HERBERT EDWARD HOL/VIAN United States Patent MANUFACTURE OF GRIDS' FOR- ELECTRON DISCHARGE DEVICES Albert Horace Atherton, Southall, aridHerbe'rtEdward Holman, West Drayton, En'glandfa'ssignors'to Electric & Musical Industries Limited, Hayes,'Middlesex, England, a British company Application September 9, 1953, Serial No. 379,166

Claims priority,'application GreatBritain September 13, 1952 3 Claims. (Cl. 29-2517) This invention relates tothe-manufacture ofgr-idsfor electron .discharge devices.

In thermionic valves the grid surrounding-the cathode oranother electrode such .as a further grid .is usually formed by winding wire around a pair of spaced apart support rods. at very high frequencies a very small and accurate spacing is required between the grid-and'thecathode' or other electrode. The. grid wire employed .must of necessity be of a very small diameter, such as less than 0.02'mm.,

and must be wound-under tension on a very rigid frame to maintain the dimensional accuracy required. -Heretodifliculty owing to the smalldimensions of the frame and the requirement for the thickness of the frame to be maintained witha' high degree-of accuracy, sin'ce'it is the thickness of the frame which mainly determines the spacing of the grid wire from opposite surfaces of the cathode. Furthermore the frame must be constructed so that after winding the grid thereon a cathode or other electrode can be inserted into the interior of the grid.

The object of the present invention is to provide an improved method of manufacturing a grid wound on a frame in which the latter is formed in such a mannerthat consistent accurate dimensions can be obtained.

According to the invention there is provided a method of making a grid for an electron discharge device which comprises forming a frame by securing together a pair of frame members each having side portions spaced apart by cross-bars at opposite ends thereof with the side portions abutting one another and with the cross-bars at opposite ends spaced apart to enable another electrode to be inserted through said spaced cross-bars, subjecting the sides of said frame which are formed by said side portions to a pressing operation to impart a required thickness to said sides and then winding a grid around the sides of said frame.

In manufacturing the frame the latter may be formed from two identical frame members which may be pressings made from molybdenum and after securing the frame members together, preferably by brazing, the thickness of the side portions of the frame are made slightly oversize so that on subjecting the sides of the frame to said pressing operation they are reduced to the required dimensions and in this manner it is possible to maintain an accuracy of 10.00025 inch.

In order that the said invention may be clearly understood and readily carried into effect, it will now be more fully described with reference to the accompanying drawings, in which:

Figure l illustrates a side elevation view of a grid in accordance with the invention,

Figure 2 is a cross-section view taken along the line 2-2 of Figure 1, and

Figure 3 illustrates a grid in accordance with the invention in an electron discharge device.

However, in thermionic valves for use -fore the manufacture of a rigid frame has presentd 'some 2,845,691 "Patented Aug. 5, 1958 As shown in Figures 1 and'2 ofthe drawings, the

.grid is formed by winding grid wire, a fewturnsof which are indicated at 1 in Figure 1 around a frame 2 of molybdenum. The frame-2 in the embodiments shown :is made from two identical pressingsfi-and' 4 forming a ,pairor frame members, each frame member having .ship. The frame members may be provided with a' 0.240 inch and the width ofthe sidelpor'tions 5 and 6 arid the cross-bars 0.040 inch. Priorto subjecting the sides of .the' frame to said: pressing .operation the thickness of the sides may be0l032 to 01034 inchand after pressing the thickness of-the sides is reduced to a.thickness of 0.0315 inch $000025 inch. .Afterforming the frame in the {manner aboveedescribed, :the,grid.1 is wound thereon, the..grid-. having," for example, 400' turns per inch and being wound with wire of.0'.004 inchdiameter.

"The cross-bars 7- and 8 .at each end of said .frame are spaced apart from one another, .as ,W'illQbe .observed from"Fi'gure2 of the drawings, so 'that after winding the grid an indirectly heated cathode 9 can be inserted into the interior of the wound grid. The width of the cathode may be 0.120 inch and its thickness 0.0265 inch.

The side portions 5 and 6 preferably extend beyond the cross-bars 7 and 8, so that the extended portions can serve as locating lugs for locating the grid in apertures 10 formed in a pair of insulating supports 11. The cross-bars 7 and 8 may be arranged to abut againstthe surfaces of the insulating supports 11 so that the grid is prevented from axial movement relatively to the insulating supports. The insulating supports 11 are also provided with apertures 12 in which the ends of the cathode 9 are located.

Figure 3 of the drawings illustrates a grid in accordance with the invention in an electron discharge device of the triode type, the electrode structure shown therein comprising a pair of support rods 13 on which the insulating supports 11 are assembled. Additional support rods are carried by the insulating supports 11 as indicated at 14, these additional support rods serving to support between the insulating supports 11 an anode 15 which is formed with a re-entrant portion 16 which is disposed close to the grid 1, a similar anode being provided on the opposite side of the device to that shown electrodes are electrically connected in known manner.

The wire from which the grid is wound is preferably tungsten wire and is gilded before winding by drawing the wire through a molten bead of gold in a reducing atmosphere such as hydrogen. The use of tungsten wire with a frame made of molybdenum is advantageous since the coefficients of expansion of these metals is substantially the same. The gilded wire is then wound on the frame under tension and the first few turns and the final few turns of the grid which may lie over the cross-bars may be temporarily held in position by means of a suitable volatile cement, such as a nitrocellulose cement. In order to secure the individual turns of the grid wire to the frame, the wires and the copper-plated frame are heated to a temperature of about 700 to 1000 C. for a short time in order to braze the gilded wire to the copper plated frame. Although the temperature referred to is below the melting point of either copper or gold, brazing is efiected at this temperature due to the formation of a gold-copper eutectic alloy. By copper plating the frame as aforesaid and gilding the wire'the brazing temperature for the securing of the wire in position is substantially lower than that required for ordinary gold brazing, with the result that the grid convolutions can be maintained at a higher tension.

Although the grid is shown in Figure 3 as applied to a triode valve where it serves as the control grid, it is to be understood that a grid in accordance with the in ention can be employed in other types of electron discharge devices. For'example it could be employed as the screening grid in a tetrode valve.

What we claim is:

1. A method of making a frame type grid electrode for an electron discharge device which comprises forming a frame having sides and cross-bars consisting of a pair of frame members eachhaving side portions spaced apart by cross-bars at opposite ends thereof, bending over on themselves each of the side portions, arranging said frame members with said bent over portions contacting one another and with the cross-bars at opposite ends spaced apart, connecting said side portions together, subjecting the sides of said frame to a pressing operation to compress said bent-over portions and to impart a predetermined thickness to said sides and then winding a grid around the sides of said frame.

2. A method of making a frame type grid electrode for an electron discharge device which comprises forming a frame having sides and cross-bars consisting of a pair of frame members each having side portions spaced apart by cross-bars at opposite ends thereof, bending over on themselves each of the side portions, arranging said members with said bent over portions contacting one another and with the cross-bars at opposite ends spaced apart, brazing said side portions together, subjecting the sides of said frame to a pressing operation to compress said bent-over portions and to impart a predetermined thickness to said sides and then winding a grid around the sides of said frame.

3. A method of making a frame type grid electrode for an electron discharge device which comprises forming a frame having sides and cross-bars consisting of a pair of frame members each having side portions spaced apart by cross-bars at opposite ends thereof, bending over on themselves each of the side portions, arranging said members with said bent over portions contacting one another and with the cross-bars at opposite ends spaced apart, brazing said side portions together, subjecting the sides of said frame to a pressing operation to compress said bent-over portions and to impart a predetermined thickness to said sides, providing a coating of copper on said frame, winding a gilded grid wire around said frame and brazing the wound grid to said frame by heating the frame and the turns of said grid.

References Cited in the file of this patent UNITED STATES PATENTS 2,175,704- Schade Oct. 10, 1939 2,549,551 Walsh Apr. 17, 1951 2,592,549 Ekstrand et al. Apr. 15, 1952 FOREIGN PATENTS 348,360 Great Britain May 14, 1931 586,676 Great Britain Mar. 27, 1947 

